1. Field of Invention
This invention relates in general to magnetic recording and reading systems for disk files and, in particular, to improved digitally controlled read/write channels for disk files.
2. Cross-Referenced Applications
Ser. No. 495,322, filed concurrently herewith in the name of Harr, entitled "Integrated Circuit Filter with Adjustable Characteristics", and commonly assigned, describes a current controlled integrated circuit filter that may be employed in the recording channel of the present invention.
3. Description of the Prior Art
Disk files are used extensively for the storage of data in data processing systems. The term "recording channel of a disk file" includes the "write" circuits and the "read" circuits. The write circuits function to convert a byte of binary data as it exists in a register of the file to the flow of current through the write coil of a magnetic transducer which produces magnetic flux that magnetizes the disk surface in some predetermined pattern which represents the data. The "read circuits" function to convert the current in the read winding of the magnetic transducer which is induced as the read winding is moved relative to the recorded flux pattern to a byte of binary data in another register in the file. While the "read" and "write" functions of the read/write channel both generally involve analog and digital type circuits, the "read" circuits are predominantly implemented in analog type circuits.
Generally, the write channel only includes an analog write amplifier circuit with the remaining signal processing and control circuits being digital in nature. In contrast, the read channel includes an analog read amplifier and an analog variable gain amplifier circuit which is connected to the read amplifier by a direct current (DC) blocking capacitor. The output of the VGA or variable gain amplifier circuit is generally supplied to the data detector circuit through a passive filter network and another amplifier. Depending on the type of signal detecting process employed, e.g., peak detecting, slope detecting, etc., the read channel detector generally also includes a number of analog functions such as signal differentiation, threshold setting circuits, delay circuits, and a single shot circuit which eventually converts the information contained in the analog signal to a binary digital output signal that is then stored in a static register.
Because of the frequency dependent nature of the analog type circuits, a recording channel must necessarily be tailored to the operating specifications of a given disk file, specifically those which are frequency and amplitude dependent, such as recording density, data rate, rotational speed of the disks, etc.
In the past, where the signal processing and control circuits were implemented in circuit technologies involving discrete components, the problem of redesigning the recording channel when, for example, the data rate increased, could be achieved in a relatively short period of time because of the nature of discrete component technology. As integrated circuit technologies have improved, a tremendous cost advantage has been established for implementing circuits in LSI (large scale integration) or VLSI (very large scale integration) technology. Implementing circuit functions in VLSI technology, however, does require the circuit designer to specify the various design parameters prior to actual implementation and imposes a rather long turnaround time, for example, six months, to effect a subsequent change in even one of the parameters in the circuit, no matter how trivial that change may be. Since many of the design parameters of the recording channel are so interdependent on other areas of the disk file that are being developed in parallel with the recording channel, provision must generally be made external to the IC chip set to modify or trim certain parameters which are built into the chip. As a result, the integrated chips for the recording channel are surrounded by AC coupling capacitors, filter inductors and capacitors, and level setting resistors which cost card and module space and increase the manufacturing cost of the recording channel. These external components also tend to degrade the overall operation of the read/write channel. The flexibility of such an approach is also limited to merely tailoring the basic channel characteristics within relatively narrow ranges and cannot be employed in connection with another disk file having different frequency dependent characteristics.
It would, therefore, be advantageous to have a recording channel VLSI implementation in which minor adjustments could be made to the various circuit functions within the channel to tailor the various functions to the particular channel and also have the ability to change within relatively large ranges the operating characteristics of the circuits so that, basically, the same recording circuits could be employed in different disk files. The present invention provides such a recording channel.
The present invention is directed to a recording channel implementation in which the analog circuits of the recording channel are implemented in VLSI technologies and controlled by a microprocessor through various control circuits which are also implemented in the same VLSI technology on the same chip, thereby eliminating substantially all of the external components employed in the prior art recording channel implementations.